reserve A for QC-alphabet;
reserve k,n,m for Nat;
reserve P for QC-pred_symbol of A;
reserve F for Element of QC-WFF(A);
reserve Q for QC-pred_symbol of A;
reserve F, G for (Element of QC-WFF(A)), s for FinSequence;
reserve p for Element of QC-WFF(A);
reserve F for Element of QC-WFF(A);

theorem Th17:
  for k being Nat, P being QC-pred_symbol of k, A holds P
  `1 <> 0 & P`1 <> 1 & P`1 <> 2 & P`1 <> 3
proof
  let k be Nat, P be QC-pred_symbol of k, A;
  reconsider P9 = P as QC-pred_symbol of A;
  P9`1 = 7+the_arity_of P9 by Def8;
  hence thesis by NAT_1:11;
end;
